Traditional Circuit Switched (CS) telecommunication networks, such as Public Switched Telecommunication Network (PSTN), Integrated Services Digital Network (ISDN) or Public Land mobile Network (PLMN) implemented as e.g. a Global System for Mobile communications (GSM) do nowadays co-exist with recently developed Packet Switched (PS) telecommunication networks, such as the Internet where e.g. Voice over Internet Protocol (VoIP) voice calls are applied.
VoiP cells are considered as an inexpensive way to communicate while CS calls are considered to be more expensive but to have a better, generally worldwide coverage. Furthermore a substantial amount of CS network operators offer mobile services, extending the attractiveness of CS communication.
As both PS- and CS-networks offer substantial benefits for a user of a communication device, integration of both networks into one telecommunication network took off in the early nineties by means of Media Gateway (MGW) devices connecting CS and FS networks thereby enabling calls between both networks.
Voice calls initialized by means of a terminal at a CS network towards a terminal residing in PS a network could be made in the way described in patent application WO 2007/005124 A2. This patent application describes a method and system where a user, after authentication to a server, receives a contact list at his terminal, which list is applied to select a name of a person to be called at a PS network.
The patent application does not disclose how to initialize voice calls to a CS terminal, while benefiting from the contact list which is maintained at a server residing at the PS network.
In case PS- and CS networks are integrated into a one telecommunication network, a user requiring communication to a party has to select either the CS- or PS-network depending where a communication device of the party is attached to. In case the party has a communication device attached to the PS network, a call setup has to be executed differently compared to a call setup where the party applies a communication device attached to a CS network, requiring additional knowledge and practice of the user to handle the user interface at his terminal.
Voice calls, regarded as a traditional communication method, provide a high level of interactive communication. A less interactive communication method known as messaging is implemented on e.g. computers and mobile CS terminals by application of an Instant Messaging and Presence (IM&P) protocol as defined by the Internet Engineering Taskforce (IETF). Use of both forms of communication methods at one terminal device requires different user practice as to control the user interface of his terminal, requiring still further knowledge and practice.
Present CS- and PS-networks comprise a number of devices and protocols that are standardized and operate with standardized communication protocols. A method to initialize a call such as in the prior art document above would require an additional server for maintaining the contact list. Installation of additional servers to a communication network increases complexity of the network and increases maintenance efforts.